The use of various thermoplastic resins to make films and nonwoven fabrics is well known. In particular, propylene-based polymers and copolymers (sometimes referred to as propylene-based elastomers) are well known in the art for their usefulness in a variety of applications, including the manufacture of films and nonwoven fabrics. Such films and fabrics have a wide variety of uses, such as in medical and hygiene products. Elastic laminates, especially those used as diaper waist bands, leg cuffs, and elastic stretch engines, have been constructed from an elastic laminate that comprises a film inner layer with outer fabric or nonwoven facing layers.
In such elastic laminates, the extensibility of the laminate is typically governed to a large extent by the properties of the elastic film layer. For diaper applications there is a customer preference for a soft-stretch, where the laminate when extended shows a load that increases initially but remains relatively unchanged with additional extension. Soft-stretch laminates are particularly desirable for infant diaper applications, so that when an adult fastens the diaper on the infant they will not need to apply a high force to extend the elastic laminate.
Examples of elastic laminates include an inner film layer of an elastic styrenic block copolymer (SBC) compound laminated between facing layers of polypropylene based nonwoven fabrics. However, in such laminates the SBC layer is relatively incompatible with the PP facing layer. Therefore, adhesive tie layers are needed to provide a good bond between the facing fabric layers and the elastic film layers. However, adhesive tie layers increase the complexity of the lamination process and add overall cost to the production process.
U.S. Pat. No. 7,951,732 describes elastic laminates and articles that include one or more facing layers comprising thermoplastic resins and propylene-based polymer and one or more inner layers comprising propylene-based polymers.
EP Publication No. 0964890 describes elastomer compositions comprising a crystalline polyolefin, an elastomeric ethylene/alpha-olefin polymer, a plasticizer, and a material that provides an increase in wet coefficient of friction.
U.S. Patent Application Publication No. 2013/0053479 describes fibers formed from compositions comprising thermoplastic polymers and oils.
U.S. patent application Ser. No. 14/285,050 describes stretch-cling films comprising propylene-based elastomers and polyalphaolefins.
Additional background references include U.S. Pat. Nos. 7,122,584; 7,335,696; 7,662,885; 7,645,829; U.S. Patent Application Publication No. 2006/0135699, 2009/0043049, and 2013/0281596; and PCT Publication Nos. WO2006/118807 and WO2009/035579.
While the above references provide a variety of different polymers and films, none provide for an elastic laminate having the desired soft-stretch. Therefore, there is a need for elastic laminates having good soft-stretch and elasticity and that are constructed from compatible inner layer films and outer facing layers that do not require an adhesive tie layer therebetween.